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\f0\b\fs24 \cf2 El Ni\'f1o Might Speed Up Climate Change\
\b0 byTim Vernimmen\
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\cf2 Dec. 1, 2017 \'96 Every 2 to 7 years, abnormally warm water in the Pacific Ocean causes an atmospheric disturbance called El Ni\'f1o. It often makes extreme weather worse in various places around the world: greater floods, tougher droughts, more wildfires. Now scientists have new evidence indicating El Ni\'f1o conditions might also add extra CO
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\fs24 to the atmosphere, as well as lessen the ability of trees to absorb the greenhouse gas.\
By certain measures, the most recent El Ni\'f1o, which held sway in 2015 and 2016, was 1 of the 3 strongest on record, along with episodes in 1982\'961983 and 1997\'961998. Although its impacts on land were not clearly stronger than those of the other events, it appears it was the major culprit for a record increase in CO
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\fs24 \'a0during its reign. \'93CO
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\fs24 emissions from fossil fuels and industry did not really change from 2014 to 2016,\'94 says climate scientist Pierre Friedlingstein at the University of Exeter in England, and an author of the 2017 carbon budget report released by the Global Carbon Project in November. So the dramatic increase, he says, must be due to how land and sea responded to El Ni\'f1o.\
A recent article in\'a0
\i Science,
\i0 \'a0about satellite measurements made during El Ni\'f1o by NASA\'92s Orbiting Carbon Observatory-2, showed that most of the extra CO
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\fs24 originated in the tropics. It also suggested that each tropical region contributed a similar amount of CO
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\fs24 \'a0as in other strong El Ni\'f1o years, each in its own way. In South America's Amazon, for example, slower-growing plants absorbed less CO
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\fs24 , whereas in Africa, plants and soils released more of the gas.\
The observations are based on satellite readings of CO
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\fs24 , carbon monoxide (CO, which is released by wildfires) and other factors like the fluorescence of the chlorophyll in plant tissues (which reflects growth). But scientists would want some ground-truthing to prove El Ni\'f1o conditions in the tropics boosted atmospheric CO
\fs20 2
\fs24 \'a0levels. In the past, field data from plants and soils during an El Ni\'f1o has been thin, but in 2015 researchers were better prepared.\
Ecosystem scientist Yadvinder Malhi, at the University of Oxford, and colleagues analyzed data from 54 tropical forest plots in Ghana, Gabon, Malaysia, Brazil and Peru, which they presented at a recent meeting that Mahli organized in London. The ground data confirmed what the satellite data had suggested: the tropics are key. The amount of CO
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\fs24 \'a0released from the sites predicted the atmospheric levels \'93surprisingly well,\'94 according to Malhi. \'93In contrast to long-term climate change,\'94 he said at the meeting, \'93everybody agrees that El Ni\'f1o makes the amount of CO
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\fs24 \'a0in the atmosphere go up faster than usual.\'94\
The next question was how much each continent contributed. Malhi says the Amazon appears to be the biggest player. \'93Africa always emits a lot of CO
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\fs24 , since it has a lot of wildfires, especially in the savannas. But its tropical forests and savannas didn\'92t behave very differently from other years,\'94 he says. In the Amazon, however, \'93the emissions seemed largely due to respiration: CO
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\fs24 released from plants, decaying logs and the soil.\'94\
Further analysis will allow Malhi\'92s team to distinguish between those different sources, which is important for predicting longer-term impacts. If, for example, it turns out the extra CO
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\fs24 \'a0released during El Ni\'f1o is largely due to microbial activity in soils and decomposing plant material, Malhi says, \'93I wouldn\'92t expect it to last\'94 as the world warms further. If the increase is coming from the plants because they are respiring more, that might be a signal of long-term stress that may continue to raise CO
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\fs24 \'a0levels.\
As a carbon booster, El Ni\'f1o could hasten rising temperatures, bringing the world to dangerous thresholds sooner than thought. It could also enhance feedbacks between climate and vegetation that could reduce plants\'92 ability to absorb CO
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\fs24 \'a0in non-Ni\'f1o years as well. If bad droughts or wildfires kill many trees, for example, forests and their carbon sequestering potential may take centuries to recover, if ever.\
Wildfires are a big concern. They were not quite as pervasive in 2015\'962016 as they were in 1997\'961998, when they were the most important global source of extra CO
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\fs24 . In 2015\'962016, \'93a bit of rain at just the right moment prevented the Southeast Asian peat forest fires from spreading as widely as they did 2 decades ago,\'94 says climate scientist Guido van der Werf at Vrije University Amsterdam. \'93Nevertheless, fire is a growing problem in the region.\'94 Drought and heat make the forests more vulnerable. Wildfires release a lot of CO
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\fs24 , and they also eliminate the trees that might store more CO
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\fs24 \'a0in the future.\
Even absent fire, El Ni\'f1o might be killing trees. In northern Australia's remote Gulf of Carpentaria, more than 18,200 acres of mangrove vegetation died during the last El Ni\'f1o, due to a convergence of severe drought and unprecedented high temperatures. Death by drought may threaten trees in the Amazon as well.\
To transport water from roots up to leaves, trees depend on tension created by the difference in water availability in the soil and the atmosphere, says plant physiologist Lucy Rowland at Exeter. \'93If it is very dry, however, that tension can get too high,\'94 she says. \'93If that happens, the column of water in the trees\'92 transport vessels breaks. Then air gets in, blocking water flow like a bubble in your central heating system does.\'94\
The only way trees can fix this problem is by growing new vessels\'97if the lack of water does not kill them first. Rowland is also investigating whether severe drought hampers the ability of tropical vegetation to absorb more CO
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\fs24 \'a0as the atmospheric concentration rises. Right now, she says, the way climate models incorporate vegetation\'92s response to drought is too simplistic.\
For now, tropical trees appear to have returned to normal, their ecosystems absorbing more CO
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\fs24 \'a0than they emit, Friedlingstein concludes. Unfortunately, man-made emissions have returned to their old status as well. \'93After 2 years of stability,\'94 he adds, \'93they are going up again.\'94\
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\cf2 www.scientificamerican.com/article/el-nino-might-speed-up-climate-change/?utm_source=Daily+Climate&utm_campaign=10c7ebe992-RSS_EMAIL_CAMPAIGN&utm_medium=email&utm_term=0_9c8bdfd977-10c7ebe992-99361585}